This project is directed toward an understanding of the functional significance of evolutionary changes in nucleic acids. Specific questions will center around the organization, function and evolution of Drosophila (1) mitochondrial DNA; (2) ribosomal DNA spacer sequences; (3) transcriptional units; (4) muscle actin gene(s). Experimental approaches include morphological (electron microscopy), genetic, cytogenetic, biochemical and molecular analyses. Examples of specific experiments are: (1) to test the physical association of transcriptional and translational processes in mitochondria, and the similarity of these processes to those in bacteria; (2) investigate the unusually long non-transcribed spacer sequences between ribosomal RNA genes that are transcriptionally active during oogenesis in Drosophila; (3) determine the organization and evolution of transcriptional units in Drosophila species that are expected to have genes of different size; (4) locate and study the organization, multifunctionality , and evolution of Drosophila actin genes. Does the same gene(s) specify muscle actin as well as microfilament "actin"? (5) to test the periodicity of repeat sequences in specific euchromatic genes; (6) to determine the structure of telomeres in polytene chromosomes.